Your friend has a font feature called "strikeout" turned on.
Assuming he doesn't have it selected in his software,
there are several possible causes.

The documents
Some software use strikeout to signify the print region is
outside of the printer's paper margins.  This is especially
prevelant with labels as it doubles as an alignment mask
while alerting you that the label may be truncated, so that
you don't mistakenly use it.

The feature could be turned on in the printer, causing it to
appear on all print jobs.  See the manual about using the
the printer's front panel menu.

The printer could be malfunctioning.  Improper cable, wrong
protocol, wrong driver, or faulty printer circuitry can all cause
strange font substitutions.
Tom Turak
----------
From: vincent v. young
Sent: Monday, June 28, 1999 7:25 PM
Subject: [PCBUILD] Please eliminate line out on hp printer
a friend has an hp laser printer which prints a line through the
the characters.

                         PCBUILD's List Owner's:
                      Bob Wright<[log in to unmask]>
                       Drew Dunn<[log in to unmask]>